The intensity of x-ray which has transmitted a material is detected by radiating x-ray to the material placed between an x-ray generator and an x-ray detector. By reconstructing, through a computer, the intensities of the x-rays which have been shot while rotating the material, a distribution of x-ray absorption inside the material cross-section can be obtained, which is called x-ray tomography computed tomography.
The x-ray tomography is a typical non-destructive method of analyzing material, the absorption coefficient of the x-ray being known as a function of density of the material. An x-ray tomography image is a result obtained by converting the difference among absorption coefficients to a shaded image, which can be decoded by trained staffs. The method, however, resorts to a qualitative decision through a naked eye, which can include errors due to the experience and subjective feeling of a person and has limitation in its reproducibility.
U.S. Pat. No. 5,774,520 provides method of obtaining clear x-ray tomography image by using a single gamma ray excluding scattering, but just show the density difference as the difference between absorption coefficients failing to provide actual quantitative density distribution.